1. Field of the Invention
The present invention relates to machine tools processing metallic materials. In detail, the invention relates to a machine tool having a bed with a table, a column provided on the bed, and a spindle head provided on the column.
2. Description of the Related Art
Nowadays, a machine tool having a bed with a table, a column mounted at the back portion of the bed and a spindle head provided on the column (column type machine tool), the bed and the column are made in high stiffness so that the accuracy in vertical motion of the spindle head and in rotational motion of the main shaft supported by the spindle head can be ensured.
Meanwhile, recently in metal processing, when the main shaft is supported in a rotatable manner with air bearing and the main shaft is rotated at a speed of several thousand revolution per minute (for instance, fifty to seventy thousand rpm.), it is recognized that a high-efficiency processing in the feed speed for cutting at several meter per minute can be achieved.
When such a high speed rotation spindle head is applied on a column type machine tool, there arises a problem that high finish surface accuracy can not be ensured due to vibration caused by the high rotation of the main shaft.
In order to solve the problem, the bed and the column can be constructed in higher stiffness, but it is not practical because it is still insufficient and results in an increase in size and weight of the whole machine.
It is an object of the present invention to solve the problem and to provide a machine tool to ensure a high finish surface accuracy without an increase in size or weight.